Calcium, Phosphate, and Parathyroid Hormone (PTH), Serum — Calcium Challenge Test
Measures calcium, phosphate, and PTH in blood during a prescribed calcium challenge to help evaluate parathyroid function.
["This test shows how the parathyroid glands respond to a controlled calcium challenge."]
Key facts at a glance
- LOINC
- 1380-5
- Short code
- Calcium/Phos PTH Chall Ser
- Synonyms
- Calcium/Phos PTH Chall Ser
- Category
- thyroid
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 8.5
- Ref high
- 10.5
- Critical range
- 6 N/A – 14 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82310
- SNOMED
- 110744001
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What is this test?
This blood test measures calcium, phosphate, and parathyroid hormone (PTH) during a calcium challenge. It helps clinicians assess how the parathyroid glands respond when the amount of calcium in the blood is deliberately increased.
Why might I need this test?
It may be used when hyperparathyroidism or another cause of abnormal calcium levels is suspected but the results of standard tests are unclear. The pattern of calcium, phosphate, and PTH before and after the challenge can provide information about parathyroid function.
How is the test performed?
Blood is collected before and at specified times after a controlled dose of calcium is given under a healthcare professional's supervision. Each blood sample is analyzed for calcium, phosphate, and PTH, and the changes over time are interpreted together.
How do I prepare for the test?
Follow your clinician's instructions about fasting, calcium supplements, vitamin D, and other medicines. Do not take extra calcium before the test unless your care team specifically tells you to do so, because it may affect the results.
Reference range
Adult: 8.5-10.5 mg/dLN/A
No special preparation required. Stay well hydrated.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The way calcium, phosphate, and PTH change during the challenge may suggest normal, excessive, or inadequate parathyroid response. Abnormal results can also occur with kidney disease, vitamin D deficiency, medication effects, or other conditions affecting calcium balance. Results should be interpreted by a clinician using the full examination and other laboratory findings.
Short name
Calcium Challenge Test
Frequently asked questions
Does the challenge test give me too much calcium?
Why are calcium, phosphate, and PTH checked together?
Do I need to fast for this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy